Variation in the ability to form ectomycorrhizas in the F1 progeny of an interspecific poplar (Populus spp.) cross

The aim of this study was to determine the existence of a genetic basis for the ability to form ectomycorrhiza on a model angiosperm tree (Populus, poplar). Parental clones and 18 progeny from a controlled interspecific cross between Populus deltoides and Po- pulus trichocarpa were grown in a glasshouse and inoculated with mycelium of the ectomycorrhizal fungus Laccaria bicolor. Three months after inoculation, the percentage of mycorrhizal root tips was determined for each inoculated plant. The data indicate variability in the ability to form ectomycorrhizas among the F1 progeny, including individual progeny which are different to either parent. This suggests a genetic basis for mycorrhiza formation. Accepted: 6 November 2000     

Manganese reduction in the rhizosphere of mycorrhizal and nonmycorrhizal maize

The influence of rhizosphere microorganisms and vesicular-arbuscular (VA) mycorrhiza on manganese (Mn) uptake in maize (Zea mays L. cv. Tau) plants was studied in pot experiments under controlled environmental conditions. The plants were grown for 7 weeks in sterilized calcareous soil in pots having separate compartments for growth of roots and of VA mycorrhizal fungal hyphae. The soil was left either uninoculated (control) or prior to planting was inoculated with rhizosphere microorganisms only (MO-VA) or with rhizosphere microorganisms together with a VA mycorrhizal fungus [Glomus mosseae (Nicol and Gerd.) Gerdemann and Trappe] (MO+VA). Mycorrhiza treatment did not affect shoot dry weight, but root dry weight was slightly inhibited in the MO+VA and MO-VA treatments compared with the uninoculated control. Concentrations of Mn in shoots decreased in the order MO-VA > MO+VA > control. In the rhizosphere soil, the total microbial population was higher in mycorrhizal (MO+VA) than nonmycorrhizal (MO-VA) treatments, but the proportion of Mn-reducing microbial populations was fivefold higher in the nonmycorrhizal treatment, suggesting substantial qualitative changes in rhizosphere microbial populations upon root infection with the mycorrhizal fungi. The most important microbial group taking part in the reduction of Mn was fluorescent Pseudomonas. Mycorrhizal treatment decreased not only the number of Mn reducers but also the release of Mn-solubilizing root exudates, which were collected by percolation from maize plants cultivated in plastic tubes filled with gravel quartz sand. Compared with mycorrhizal plants, the root exudates of nonmycorrhizal plants had two fold higher capacity for reduction of Mn. Therefore, changes in both rhizosphere microbial population and root exudation are probably responsible for the lower acquisition of Mn in mycorrhizal plants.     

Effect of vesicular arbuscular mycorrhiza and soluble phosphate onAbelmoscus esculentus (L.) Moench

Summary Effect of VA mycorrhiza and soluble phosphorus onAbelmoscus esculentus (L.) Moench was studied in a phosphorus deficient sandy loam soil with pH 5.5. The mycorrhizal infection and spore production were reduced by an increase of added soluble phosphorus. Root, shoot and total plant dry weight were significantly greater in mycorrhizal plants than in non-mycorrhizal controls, at all levels of added soluble P. Mycorrhizal dependency was found to decrease with increase in added soluble P. Depression of growth, as compared with growth at 100% was noticed in mycorrhizal plants when 200% of the recommended P was added.     

接种菌根真菌对青冈栎幼苗耐旱性的影响

利用丛枝菌根真菌摩西球囊霉(Glomus mosseae)、根内球囊霉(Glomus intraradices)和外生菌根真菌彩色豆马勃(Pisolithus tinctorius)对石漠化地区造林树种青冈栎(Cyclobalanopsis glauca)幼苗进行接种试验。在大棚盆栽条件下模拟土壤干旱胁迫,研究菌根真菌对青冈栎生长和耐旱性的影响。结果表明:在土壤干旱条件下,接种菌根处理植株生物量显著高于未接种处理(P0.05),菌根依赖性随土壤水分含量降低而升高;未接种处理植株叶绿素含量在土壤干旱条件下显著降低(P0.05),除接种Pisolithus tinctorius处理外,其它接种处理叶绿素含量无显著变化。土壤干旱使植株体内脯氨酸和可溶性糖含量上升,在中度干旱条件下,接种处理可溶性糖含量均显著高于对照处理,接种Glomus intraradices、Pisolithus tinctorius处理脯氨酸含量显著低于对照(P0.05);在重度干旱条件下,接种Glomus mosseae和Glomus intraradices处理可溶性糖含量显著高于对照处理(P0.05),而相应的脯氨酸含量显著低于对照处理。当土壤水分含量在田间持水量55%—65%时,接种处理植株SOD、POD和CAT酶活性显著高于未接种处理(P0.05),在土壤水分含量降至35%—45%时,Glomus mosseae和Glomus intraradices处理SOD酶活性显著高于对照,并且所有接种处理POD酶活性均显著高于对照。此外,在水分干旱条件下,植株全磷和全钾含量也显著高于未接种处理(P0.05)。研究表明,丛枝菌根真菌和外生菌根真菌均能够侵染青冈栎幼苗根系;在干旱胁迫条件下,接种菌根真菌能够提高青冈栎植株生物量、抗氧化酶活性、增加植株可溶性糖含量和促进植株养分吸收,提高植株耐旱性,从而使青冈栎幼苗在岩溶干旱环境下更容易存活。     

Effect of drought stress on growth and water relations of the mycorrhizal association Helianthemum almeriense-Terfezia claveryi

 Plants of Helianthemum almeriense were micropropagated on MS medium and inoculated in vitro with Terfezia claveryi mycelium on MH medium and vermiculite. Mycorrhizal (M) and non-mycorrhizal (NM) plants were subjected to a drought stress period of 3 weeks in greenhouse conditions with the soil matric potential maintained at –0.5 MPa. Drought stress did not affect the amount of mycorrhizal colonization. The survival rate of M plants at the end of the drought stress period was higher than that of NM plants. The water potential was higher in M plants than in NM plants by 14% in well-watered and 26% in drought-stressed plants. Transpiration, stomatal conductance and net photosynthesis were higher in M plants than in NM plants. Transpiration was 92% higher in M plants than in NM plants under drought-stress conditions and 40% when irrigated. Stomatal conductance was 45% and 14% higher and net photosynthesis 88% and 54% higher, respectively, in M than in NM plants. Drought-stressed M plants accumulated more N, P and K than drought-stressed NM plants. Reduced negative effects of drought stress on H. almeriense by the desert truffle T. claveryi could be ascribed to specific physiological and nutritional mechanisms, suggesting that this mycorrhizal symbiosis aids adaptation to arid climates. Accepted: 7 July 2000     

The role of seed reserves in arbuscular mycorrhizal formation and growth of Leucaena leucocephala (Lam.) de Wit. and Zea mays L.

We show here that seed reserves in Leucaena leucocephala (Lam.) de Wit. and Zea mays L. (maize) are important for mycorrhizal formation and seedling growth. Seed reserve removal reduced mycorrhizal formation markedly in Leucaena but not in maize, except at 15 and 45 days after seed reserve removal. Partial or total removal of seed reserves decreased plant growth and tissue nutrient concentrations in both hosts. Nodule number in Leucaena, which was related positively to plant biomass and mycorrhizal infection levels, was reduced when one or both cotyledons were severed. Leucaena seedlings without or with partial seed reserves had higher nutrient use efficiencies throughout seedling growth. But such an effect was observed only initially in maize. Seed reserve removal increased the specific absorption rates of nutrients in both hosts. Phosphorus absorption rate was significantly and positively related to root infection levels in both Leuceana and maize. Though the growth rates of plants without seed reserves were low initially, these plants had higher growth rates during later stages. We conclude that seed reserves are not only important for seedling growth, but also for mycorrhizal formation and nodulation. Received: 15 July 1999 / Accepted: 6 December 1999     

Response ofStylosanthes guianensis to endomycorrhizal fungi inoculation as affected by lime and phosphorus applications

The nutrient concentration in the shoots ofStylosanthes guianensis (Aubl.) Sw. cultivated in a sterilized acid and dystrophic soil (Quartzipsament) amended with 4 levels of lime (0; 0.27; 0.63 and 1.10 meq Ca²⁺/100 g soil, as Ca(OH)₂), 2 levels of P (0 and 20 mg P kg^-1 soil, as KH₂PO₄) and not-inoculated or inoculated with 3 vesicular-arbuscular (VA) mycorrhizal fungi was evaluated under greenhouse conditions. The effectiveness of the different fungal species in increasing the nutrient concentration in the shoots varied with the different edaphic conditions. In general, mycorrhiza formation was associated with increases in the concentrations of most of the nutrients analyzed. Under the experimental conditions, the increments in nutrient concentration were higher overall in plants inoculated withAcaulospora scrobiculata. Inoculation ofS. guianensis with VA mycorrhizal fungi was also associated with alterations in the ratios of nutrients in the shoots, which might be important in understanding and explaining the tolerance of mycorrhizal plants to nutritional stresses such as Al and Mn toxicity.     

Inoculation with arbuscular mycorrhizal fungi alleviates harmful effects of drought stress on damask rose

This study was conducted to examine the role of arbuscular mycorrhiza fungi (AMF) in alleviating the adverse effects of drought stress on damask rose (Rosa damascena Mill.) plants. Four levels of drought stress (100, 75, 50, and 25% FC) were examined on mycorrhizal and non-mycorrhizal plants in pots filled with sterilized soil. Our results showed that increasing drought stress level decreased all growth parameters, nutrient contents, gas exchange parameters, and water relations indicators. Under different levels of drought stress, mycorrhizal colonization significantly increased all studied parameters. P_n, g_s, and E of the mycorrhizal plants was higher than those of non-mycorrhizal plants under different levels of drought stress. The increase in those rates was proportional the level of the mycorrhizal colonization in the roots of these plants. Majority of growth, nutrition, water status and photosynthetic parameters had a great dependency on the mycorrhizal colonization under all levels of drought stress. The results obtained in this study provide a clear evidence that AMF colonization can enhance growth, flower quality and adaptation of rose plants under different drought stress levels, particularly at high level of drought stress via improving their water relations and photosynthetic status. It could be concluded that colonization with AMF could help plants to tolerate the harmful effects caused by drought stress in arid and semi-arid regions.     

Mycorrhiza of the host-specific Lactarius deterrimus on the roots of Picea abies and Arctostaphylos uva-ursi

The ectomycorrhizal basidiomycete species Lactarius deterrimus Gröger is considered to be a strictly host-specific mycobiont of Picea abies (L.) Karst. However, we identified arbutoid mycorrhiza formed by this fungus on the roots of Arctostaphylos uva-ursi (L.) Spreng. in a mixed stand at the alpine timberline; typical ectomycorrhiza of P. abies were found in close relation. A. uva-ursi is known as an extremely unspecific phytobiont. The mycorrhizae of both associations are described and compared morphologically. The mycorrhiza formed by L. deterrimus on both A. uva-ursi and P. abies show typical ectomycorrhizal features such as a hyphal mantle and a Hartig net. The main difference between the mycorrhizal symbioses with the different phytobionts is the occurrence of intracellular hyphae in the epidermal cells of A. uva-ursi. This emphasizes the importance of the plant partner for mycorrhizal anatomy. This is the first report of a previously considered host-specific ectomycorrhizal fungus in association with A. uva-ursi under natural conditions. The advantages of this loose specificity between the fungus and plant species is discussed.     

Acacias respond to additions of phosphorus and to inoculation with VA mycorrhizal fungi in soils stockpiled during mineral sand mining

Three pot experiments were conducted to test the hypothesis that the growth ofAcacia spp. in stockpiled soil from two mineral sand mines, could be increased by the addition of phosphorus (P) or inoculation with VA mycorrhizal fungi. In soils from North Stradbroke Island, the dry weight of shoots ofAcacia concurrens was increased by P and by VA mycorrhizal fungi in tailings sand, while in less adsorptive topsoil dry weight was only increased at low levels of applied P. WhenA. concurrens was grown in a layer of topsoil placed over tailings sand, shoot dry weight increased, in response to inoculation with VA mycorrhizal fungi banded between the soil layers.In topsoil from Eneabba, the dry weight of shoots at low rates of applied P was increased by up to 4 times by inoculation with VA mycorrhizal fungi. The response to inoculation in both experiments was due to increases in the uptake of P by the plants.Species of VA mycorrhizal fungi differed in their ability to increase plant growth. However, in soils from both sites, the same fungal species were effective.     

Are Mycorrhiza Always Beneficial?

In this work we evaluate whether the effect of ectomycorrhiza in the early developmental stages of symbiosis establishment is detrimental or beneficial to plant productivity and whether this effect is dependent on either N nutrition or plant age. Groups of Pinus pinaster L. plants with different ages and nutritional status were inoculated with alive or dead Pisolithus tinctorius. The plants were fed with either 1.9 mM or 3.8 mM ammonium as N source. Ectomycorrhiza establishment was monitored until 1 month after the inoculation through daily chlorophyll a fluorescence measurements and the analysis of fast fluorescence kinetics O-J-I-P, biomass increment and photosynthesis. Our results show that plants react differently to ectomycorrhiza formation depending on their age (stage of development, leaf area), their initial nutritional status, and the amount of nitrogen supplied. Mycorrhiza formation was found to constitute a stress depending on the plants’ age. Increased availability of N softened or eliminated the negative impact of mycorrhiza formation. Only younger plants eventually developed a higher net photosynthesis rate when mycorrhizal. It is concluded that ectomycorrhiza formation may have a detrimental rather than a beneficial effect on plants’ productivity during their establishment and early developmental stages, and that this depends on the amount of N available to the plant, on the nutritional status and on the age of the plant. Chlorophyll a fluorescence measurements proved to be a non-destructive, non-invasive and reliable tool able to identify the first signals of plant-mycorrhiza fungi interactions.     

Some physiological responses of chickpea cultivars to arbuscular mycorrhiza under drought stress

A factorial experiment based on RCB design with three replicates was conducted to investigate changes in some physiological responses of two chickpea (Cicer arietinum L.) cultivars (Pirouz from Desi type and ILC482 from Kabuli type) to arbuscular mycorrhiza (Glomus etunicatum Becker and Gerdman) under different irrigation treatments. The experiment was carried out in the greenhouse of the Agricultural Faculty of Kurdistan University from April to August 2009. The results showed that leaf chlorophyll content of chickpea cultivars was significantly increased by arbuscular mycorrhiza (AM) under both well and limited irrigation conditions. Proline accumulation in chickpea leaves under moderate and severe drought stresses was significantly stronger than that under optimum irrigation. Inoculation of chickpea with mycorrhizal fungi caused an increase in the activities of polyphenol oxidase and peroxidase, but a decrease in the activity of catalase. Comparisons among different irrigation levels showed that chickpea plants under drought stress had the most active lipid peroxidation. Non-AM plants showed stronger lipid peroxidation under moderate and severe water stresses than AM plants. Lipid peroxidation was more active in Pirouz leaves than in ILC₄₈₂ leaves. It seems that Kabuli-type cultivar responded better to mycorrhizal symbiosis under drought stress than Desitype cultivar.     

Mycorrhizae of nitrogen-fixing legumes

Summary Most plant species form mycorrhizae, which are symbiotic fungus-root associations. Many plants can also form symbioses with specific bacteria or actinomycetes which produce root nodules and fix atmospheric nitrogen within these nodules. The tripartite mycorrhiza-legume-Rhizobium symbiosis is the subject of this review. Mycorrhizal nitrogen-fixing legumes include many important temperate and tropical crops, e.g. clover, lucerne, beans (Phaseolus andVicia), peas, soybean, cowpea, pigeonpea, groundnuts,Stylosanthes, Pueraria andCentrosema. These forage and grain legumes form endomycorrhiza of the vesicular-arbuscular (VA) type, as do most species of the Mimosoideae and Papilionoideae. Some arborescent legumes also form VA mycorrhiza, e.g.Leucaena, but many, especially the Caesalpinoideae, form mycorrhiza of the ecto-type; some, e.g.Acacia, have both ecto- and VA mycorrhiza. In some legumes, e.g. clover andStylosanthes, mycorrhizal fungi can densely colonize>70% of the root system; in others, e.g. lupins, mycorrhizal infection is usually light. Unlike theRhizobium symbiosis, mycorrhizal symbioses are essentially non-specific. The ability of mycorrhizae to increase plant uptake of phosphate and alleviate P-stress in P-deficient soils leads to increases in nodulation, nitrogen-fixation, P concentration and plant growth. Mycorrhizae also affect trace element uptake, e.g. Cu and Zn, photosynthate supply, water relations and hormonal balance in legumes. Some legumes grow so poorly without mycorrhiza as to be ecologically obligately mycorrhizal. To some extent root geometry determines the degree of dependence of a legume on mycorrhiza, because the fungal hyphae extend the absorbing surface of the root. Where a legume is growing with a non-mycotrophic plant, its competitive ability can be increased by mycorrhiza. Environmental factors and inputs of P and N fertilizer affect the effectiveness of theRhizobium-mycorrhiza interaction. Also disease tolerance of legumes can be affected by mycorrhiza. The practical impact of mycorrhiza in nitrogen-fixing legumes may be considerable. Dual inoculation of leguminous crops with elite strains of mycorrhizal fungi andRhizobium bacteria, in conjunction with minimal N fertilizer and better utilization of less P fertilizer (rock or super), is currently being studied in many countries. Inoculation techniques are being developed for exploitation on a field scale. It is hoped that further investigations, especially in low-input cropping systems, will enable the substantial potential of mycorrhiza in legume productivity to be achieved.

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Resumen La mayoría de las especies vegetales forman micorrizas, que son asociaciones simbióticas hogno-raíz. Muchas plantas pueden también formar simbiosis con bacterias específicas o actinomicetos, produciendo nódulos radicales fijadores de nitrógeno atmosférico. La simbiosis tripartita micorriza-leguminosa-Rhizobium constituye el tema de esta revisión. Entre las leguminosas micorrizables y fijadoras de nitrógeno se incluyen cultivos importantes tanto de climas templados como tropicales, como son trébol, alfalfa, judía (Phaseolus yVicia), guisante, soja, freijol, guandú, cacahuete,Stylosanthes, Pueraria yCentrosema. Estas leguminosas forrajeras o de grano forman endomicorrizas del tipo vesículo-arbuscular (VA), al igual que la mayoría de las especies de las Mimosoideae y Papilionoideae. Algunas leguminosas arborescentes comoLeucaena también forman micorrizas VA aunque la mayoría, especialmente las pertenecientes a las Cesalpinoideae forman micorrizas de tipo ecto-, aunque se han citado casos como enAcacia que poseen ambos tipos de micorrizas, ecto y VA, simultaneamente. En algunas leguminosas (trébol yStylosanthes) el hongo micorrícico puede colonizar densamente (más del 70%) el sistema radical; en otros casos (Lupinus) la infección micorrícica es por lo general leve. Al contrario de lo que ocurre conRhizobium, las simbiosis micorrícicas son esencialmente no específicas. La capacidad de las micorrizas para incrementar la absorción de P por la planta, superando así la deficiencia en fosfato de los suelos pobres en P, conduce a un incrimento de la nodulación, fijación de nitrógeno, concentración de P y crecimiento de la planta. Las micorrizas también afectan la absorción de oligoelementos como Cu y Zn, la distribución de fotosintato, las relaciones hídricas y el balance hormonal en las leguminosas. Algunas leguminosas crecen con tan poco vigor en ausencia de micorrizas que pueden considerarse, desde un punto de vista ecológico, como obligatoriamente microrrícicas. Hasta cierto punto, la geometría de la raíz determina el grado de dependencia de una leguminosa de la micorriza, ya que las hifas del hongo aumentan la superficie absorbente de la raíz. Cuando una leguminosa crece junto con una planta no micorrizable, su capacidad competitiva puede incrementarse gracias a la micorriza. Diversos factores ambientales y el aporte de fertilizantes de N y P afectan la eficacia de la interacciónRhizobium-micorriza. La tolerancia de las leguminosas a distintas enfermedades puede verse también afectada por las micorrizas. El impacto práctico de las micorrizas en las leguminosas fijadoras de nitrógeno puede ser considerable. En muchos países se está estudiando el efecto de una doble inoculación de cultivos con cepas seleccionadas de hongos micorrícicos y deRhizobium junto con un aporte mínimo de nitrógeno y una mejor utilización de menor cantidad de abono fosfatado (de roca o superfosfato). Se están desarrollando distintas técnicas de inoculación para su explotación a nivel de campo. Se espera que el resultado de estas y otras investigaciones, especialmente en el área de sistemas agrícolas de bajo consumo, permita a las micorrizas desarrollar plenamente su papel en la productividad de las leguminosas.

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Résumé La plupart des plantes forment des mycorhizes, c'est à dire des associations symbiotiques des racines avec des champignons. Beaucoup de plantes peuvent aussi former des symbioses avec des bactéries spécifiques ou des actinomycètes qui produisent des nodules racinaires et fixent l'azote atmosphérique dans ces nodules. La symbiose tripartite mycorhize-légumineuse-Rhizobium est le sujet de la présente revue générale. Les légumineuses à mycorhizes fixant l'azote comprennent un grand nombre de cultures importantes des pays tempérés et tropicaux, comme le trèfle, la luzerne, les haricots (Phaseolus etVicia), les pois, le soja, le cajou, l'arachide,Vigna sinensis, Stylosanthes, Pueraria etCentrosema. Ces légumineuses à fourrage et à graines forment des endo-mycorhizes de type vésiculaire-arbusculaire (VA), comme le font le plupart des éspèces de Mimosoideae et de Papilionoideae. Certaines légumineuses arborescentes forment aussi de mycorhizes VA, par exempleLeucaena, mais beaucoup d'entre elles, particulièrement les Caesalpinoideae, forment des ecto-mycorhizes. Certaines, comme lesAcacia, ont à la fois des mycorhizes du type VA et du type ecto. Les champignons mycorrhizogènes peuvent densement coloniser (plus de 70%) les systèmes racinaires de quelques légumineuses comme le trèfle et leStylosanthes, mais ordinairement légèrement colonisent d'autres, eg.Lupinus. A la différence des symbioses àRhizobium, celles des mycorhizes sont essentiellement non-spécifiques. L'aptitude des mycorhizes à accroître l'absorption des phosphates et à réduire la déficience en P dans les sols qui en sont pauvres a pour conséquence d'accroître la nodulation, la fixation de l'azote, ainsi que la teneur en P et la croissance de la plante. Les mycorhizes influence également l'absorption des oligo-éléments, comme Cu et Zn, l'activité photo-synthétique, les relations avec l'eau, et l'équilibre hormonal des légumineuses. Certaines légumineuses poussent si mal en l'absence de mycorhizes qu'on peut les considérer, du point de vue écologique, comme obligatoirement mycotrophiques. La géométrie des racines détérmine dans une certaine mesure le degré de dépendence d'une légumineuse par rapport au mycorhizes. En effet, les hyphes fongiques accroissent la surface absorbante de la racine. Lorsque une légumineuse pousse avec une plante non-mycotrophique, sa compétitivité peut être accrue par la mycorhization. Certains facteurs de l'environnement, ainsi que l'apport de P et de N par des engrais diminuent l'efficacité de l'interactionRhizobium-micorhize. D'autre part la résistance des légumineuses aux maladies peut être affectée par les mycorhizes. L'impact pratique des mycorhizes sur les légumineuses fixant l'azote peut être considérable. La double inoculation avec des souches sélectionnées de champignons mycorhiziens et deRhizobium bactériens, associée à un apport minimal d'engrais azoté et à une meilleure utilisation d'un moins quantité d'engrais phosophoré (de roche ou super-phosphate), est couramment étudiée dans de nombreux pays. Des techniques d'inoculation sur le terrain sont mises au point. On espère que de nouvelles recherches, en particulier sur les systèmes de culture avec faible apport exogène, permettront au potentiel des mycorhizes pour la productivité des légumineuses de se réaliser pleinement.

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Invited paper presented at the VII International Conference on the Global Impacts of Applied Microbiology, Helsinki, 12–16 August 1985. Session 10.     

Effects of vesicular-arbuscular mycorrhiza on the size of the labile pool of soil phosphate

Summary Inoculation of lettuce, onion and clover with VA mycorrhizal fungus (Glomus mosseae) increased plant yields and phosphate uptake in three soils that had been depleted in phosphate. From two soils in which the labile pool of phosphate had been labelled with³²P, the specific activity of plant phosphate was the same whether the plants were mycorrhizal or non-mycorrhizal. In a third soil (Sonning) the specific activity was lower in lettuce and clover when the plants were mycorrhizal. When the experiment was repeated with the same soil under conditions that gave lower growth rates, the specific activity was the same in mycorrhizal and non-mycorrhizal plants. The lower specific activity in lettuce and clover in the first experiment is atributed to greater release of slowly exchanging phosphate (which is not in equilibrium with the added³²P), caused by the high uptake of phosphate by the mycorrhizal plants. When they occur, lower specific activities in mycorrhizal plants may therefore not necessarily indicate a solubilizing effect of the mycorrhiza on soil phosphate.     

Stimulation of vesicular-arbuscular mycorrhiza by fungicides or rhizosphere bacteria

Stimulation of vesicular-arbuscular (VA) mycorrhizal fungi may secure the early establishment of symbiosis and benefit the host plant at an earlier stage of development. The application of Bacillus mycoides resulted in particular in the acceleration of early VA mycorrhiza formation. An increase in vigour of the symbiosis could be measured later in terms of increased sporulation of the mycorrhizal fungi after shoot removal. Natural sporulation during later mycorrhizal development was affected by combination of bacteria and just one mycorrhizal isolate. The stimulation of mycorrhizal development was shown to be non-specific with regard to host plant and the isolate of the VAM fungus. However, the effect could not be achieved in all combinations of soil types and host plants. Application of the systemic fungicides triadimefon and pyrazophos promoted VAM formation. Combinations of fungicide and bacterial treatments were not synergistic.     

Effect of dual inoculation ofRhizobium and vesicular arbuscular mycorrhizal fungi onPisum sativum

The interaction of two symbionts,Rhizobium (a bacterium) andGigaspora calospora (a VAM fungus) was studied inPisum sativum (a nodulating legume).Pisum sativum plants inoculated with VA mycorrhizal fungi andRhizobium singly and in combination responded favourably as compared to uninoculated control. Characteristically dual inoculation exerted a higher beneficial effect on shoot and root dry mass, phosphorus and nitrogen uptake, nodule formation and degree of mycorrhizal infection than either inoculum alone.     

Patterns of Root Colonization in Epacridaceous Plants Collected from Different Sites

Root colonization was studied in ten species of the Epacridaceaeat three sites in Victoria by morphological and cross-inoculationexperiments. The sites and genera chosen were Cranbourne [Epacrisimpressa Labill. andLeucopogon ericoides(Smith) R. Br.] andRye [L. parviflorus(Andrews) Lindley] on the Mornington Peninsula,and the Grampians[Astroloma conostephioides(Sond.) Benth.,A.humifusum(Cav.) R. Br.,A pinifolium(R. Br.) Benth,Brachylomadaphnoides(Smith) Benth.,E. impressa, E. impressavar.grandifloraBenth.andStyphelia adscendensR. Br.] in western Victoria. For morphologicalstudies, samples of roots from each species at each site werecleared and stained and examined microscopically. For cross-inoculationstudies, cuttings from each site were struck in potting mediuminoculated with soil from the same and other sites. The ericoidmycorrhizae in the roots of plants found at or grown in Cranbourneand Rye soils were similar. Both were significantly differentfrom the internal hyphae found in the roots of plants foundat or grown in Grampians soils, which were three times largerin diameter and formed dense coils which filled the host celland invaded adjacent epidermal cells. This suggests that morethan one fungus is involved in the relationships, that the MorningtonPeninsula sites had a different fungus from the Grampians siteand that host specificity is low. Vesicular structures werealso found commonly on plants at the Grampians site, in contrastwith other sites. Epacridaceae; root; fungus; mycorrhiza; morphology; inoculation     

Arbuscular mycorrhiza enhances preference of ovipositing predatory mites for direct prey‐related cues

Most terrestrial plants are associated with arbuscular mycorrhizal fungi but research on the effects of arbuscular mycorrhizal symbiosis on aboveground plant‐associated organisms is scarcely expanded to tri‐trophic systems. The arbuscular mycorrhizal fungus Glomus mosseae Nicol. & Gerd. enhances fitness of the two‐spotted spider mite Tetranychus urticae Koch and its natural enemy, the predatory mite Phytoseiulus persimilis Athias‐Henriot, via changes in host plant and prey quality, respectively. In the present study, it is hypothesized that gravid P. persimilis are able to recognize arbuscular mycorrhiza‐enhanced prey quality and behave accordingly. In two experiments, on leaf arenas and in cages, P. persimilis is given a choice between prey patches deriving from mycorrhizal and non‐mycorrhizal bean plants (Phaseolus vulgaris L.) as feeding and oviposition sites. The use of cages allows the manipulation of distinct patch components acting as possible cues to guide predator foraging and oviposition behaviours, such as eggs produced and traces (webbing and faeces) left by the spider mite females. Both experiments show that P. persimilis preferentially resides close to prey fed on mycorrhizal plants. The cage experiment reveals that P. persimilis uses direct prey‐related cues, mainly derived from eggs, to discern prey quality and preferentially oviposits close to prey from mycorrhizal plants. This is the first study to document that predators recognize arbuscular mycorrhiza‐induced changes in herbivorous prey quality via direct prey‐related cues.     

Changes of free and conjugated abscisic acid and phaseic acid in xylem sap of drought-stressed sunflower plants

Abscisic acid (ABA), conjugated abscisic acid, phaseic acid (PA), and conjugated phaseic acid were determined by enzyme-linked immunosorbent assay (ELISA) and gas chromatography (GC) in xylem sap of well-watered and drought-stressed sunflower plants. Conjugated ABA and conjugated PA were determined indirectly after chemical or enzymatic hydrolysis. Conjugated ABA was found to be the predominant ABA metabolite in xylem sap. In xylem sap from well-watered plants at least five, and in sap from drought-stressed plants at least six alkaline hydrolysable ABA conjugates were found. One of them corresponds chromatographically (HPLC) with abscisic acid glucose ester (ABAGE). Under drought conditions the concentrations of ABA, alkaline hydrolysable ABA conjugates, -glucosidase hydrolysable ABA conjugates, PA, and conjugated PA increased. After rewatering the drought-stressed plants, the ABA and the conjugated ABA content decreased. The possible function of the ABA conjugates in the xylem sap as a source of free ABA is discussed.     

The effect of season on VA mycorrhiza of the almond tree and of phosphate fertilization and species of endophyte on its mycorrhizal dependency

Summary Prunus dulcis (Miller), a tree which is able to develop in low fertility soils, forms VA mycorrhiza. Under glasshouse conditions the growth and P concentration in the leaf tissue of non-mycorrhizal plants, given a customary agronomic dose of P-fertilizer, were lower than those of mycorrhizal plants. The relative mycorrhizal dependency¹⁴ values of the almond tree were higher when a mixture of locally isolated (mainlyGlomus fasciculatus) was used as inoculum. These indigenous endophytes were more tolerant of added fertilizers thanGlomus mosseae taken from the pot-culture collection.The amount of VA infection and the number of Endogonaceae spores in the rhizosphere of almond trees growing in the field steadily increase from winter (the flowering season of this crop) until summer or early autumn.